Nice way to economise, this, I said, taking another sip of champagne and leaning back to admire the art nouveau chandeliers in the dining room of the Hôtel du Centre in the peaceful seaside resort of Wimereux, a 20-minute drive from the French side of the Channel Tunnel.

"Mmmm," replied my girlfriend, as she agonised over whether to order the coquille Saint-Jacques or the steak tartare for her main course.

The idea that you can save money and spoil yourself rotten at the same time was one to which we were highly receptive. But there was no denying that the maths of our upmarket booze-cruise were watertight.

Flexible day-return on Eurotunnel: £47; half-tank of petrol: £30; slap-up lunch: £50. Total outlay: about £130. Given that the most modest petit chateau costs £2 a bottle here versus £5 in London, we were about to save £36 on every crate we bought. The savings on just four crates of wine would cover all our costs, and all further economies would be pure upside.

For the exercise we had in mind, the Hôtel du Centre in Wimereux, four hours from London and a short drive away from the best hypermarket in the area, was a natural first stop.

The restaurant here, which has been run by the same family since 1890, has lost none of its provincial appeal, and the food is a treat. It's difficult to go wrong when the most expensive fixed menu costs €29 (wine and service excluded) and includes pté de foie gras for entrée and magret de canard and poached turbot for the main course. A tip, though: the wine is a bit expensive, and you might prefer to buy it by the pichet (the red is best).

After lunch, perhaps a stroll along the promenade with its turn-of-the-century facades, or a walk along the broad flat sandy beaches below. Then to Boulogne, where it would be a pity not to walk up the Grande Rue, through the medieval walls of the fortified old town, and into the ancient streets beyond. Afterwards, you might ease yourself into food-shopping mode by visiting one or two of the more upmarket places in the lower part of the town.

Beussant, in the Rue Thiers, has about 60 types of luxury chocolates to choose from, and the owner of Olivier, on the same street, is a winner of France's coveted Cheesemaker of the Year award.

But only a short drive away, in the suburb of Outreau just outside Boulogne, the Centre Leclerc beckons impatiently; given that its range of wines is the best and cheapest in the area, when we arrive it is a surprise to see almost no British numberplates in the carpark.

Let's start with the champagnes. The cheapest is €12.45 a bottle, and Veuve Clicquot costs €23.50, versus about £27 in UK supermarkets. There's also the widest choice of half-bottles I've ever seen. A half-bottle of Lanson costs €10.50, versus £12 in Waitrose. Otherwise, a magnum of Pol Roger, the Queen's chosen champagne, costs just €36. Are we dreaming?

Moving on to the reds, there is always a good selection of special offers. How about the Chateau Les Rodiers 2002, a Bordeaux Supérieur reduced from €3.29 a bottle to €2.75? There are similar bargains among the whites, and even the drinkable plonks: at €8.95 for a five-litre box, the Vin de Pays d'Oc is hardly overpriced.

But do leave time for the rest of this hypermarket - many of the groceries are either not available in Britain, or are about half the price. First the staples. Cold-pressed extra-virgin olive oil at €3.90 a litre: half what it would cost in a British supermarket. Top-quality Maille mustard at €1.63 for a 380g jar: incredibly cheap. As for mineral water, the Perrier here costs exactly half what it costs in British supermarkets, and the Badoit costs one third.

Then the luxuries: how about Gros Sel de Guérande, the ultimate salt for salt snobs, at just €1 per kilo? Or a top-quality bloc de foie gras semi-conservé at just €11 for 200g? Or 20 quails eggs for €1.90? Or two dozen oysters for €6.95?

The only sane reaction to all this can be to stuff your car full to the brim and plan a return trip as soon as possible. And here's a date for your diary: the Foire aux Vins that takes place in this store for about a fortnight starting in mid-November, at which wine-producers from all over France sell cheap - or rather even cheaper - to get cash for the next season.

I know one Englishman who'll be there, with a large car.

Way to go

Getting there:Eurotunnel (0870 5353535); day returns from £19 for car and passengers.